2008 iMac 20" that is now the kids computer crashes after 20-30 minutes of use. While playing flash games on Facebook. I updated all software, deleted all the odd stuff installed on it, and repaired permissions. Reboot, surfed the web, crashed at 32 minute mark. Fan noise abnormally loud.
Thought it was hardware. Then it got wierd
Booted into Windows XP and played Civ V for 4 hours. No problem.
Turned it off, next day booted into OS X, surfed for 37 minutes- crashed
Rebooted into XP and played Op Art War for 4 hours. No problem.
Got to be software
?????
Apple care expired over a year ago.

Since then, on Thursday I reset the SMC(?), and performed a Disk Repair from the boot disk. Disk repair found several fatal errors on the disk and repaired them.

I rebooted the computer and it ran well for about 30 minutes then I got a dialog box on the screen that says "This computer needs rebooted" in several languages and the computer was locked up. It does this now every time instead of just crashing.

I would say the hard drive is suspect. Even though Disk Utility repaired several fatal errors, there could be more. My advice is to backup what you can from both OS X and Windows XP and be prepared to change out that hard drive.

The crashes you're receiving are known as kernel panics which usually indicate a hardware error.

thats what I was fearing. I looked at a couple youtube tutorials about taking this Mac apart, and it looks far from easy. I'm gonna break the screen.
the local repair center wants $300 or more to swap a drive, $80 just to look at it. Don't know if its worth it.
It's just weird that in Windows it seems to function normally. Thats why I was hoping there was some bizarre thing happening. The DUKROM or SMERSH controller needed reset or something.
Theres no data to back up, its the kids computer. Was thinking about trying a clean install, but if it hangs during an install im screwed

Removing the display from an iMac is certainly not a simple process, however, with the right tools and instructions, you can do it yourself. The ifixit web site sells the glass suckers and proper torx drivers that are needed. They also provide the best step by step that I know of.